Variable contour propeller blades



Dec. 29, 1959 R. A. FANTI VARIABLE coNTouR PROPELLER BLADES Filed Feb.11

ATTORNEY UnitedStates Patent O VARIABLE CONTOUR PROPELLER BLADES Roy A.Fanti, Springfield, Mass., assignor to United Aircraft Corporation, EastHartford, Conn., a corporation of Delaware Application February 11,1957, Serial No. 639,377

1 Claim. (C1. 17o-160.24)

This invention relates to propellers and more specically to propellershaving variable contour blades.

It is an object of this invention to provide propellers having bladeswhich achieve high lift at low angles of attack. l

It is another object of this invention to provide propellers havingblades Ahaving improved stall flutter boundaries as compared to iixedcontoured or cambered blades.

It is a still further object of this invention to provide exible bootsover a substantial span of the blades on the upper and lower majorsurfaces near the trailing edge of the blade.

It is a still further object of this invention to provide flexible bootswhich can be selectively inflated to asymmetrically vary the prole ofthe trailing edge of the blade.

These and other objects of this invention will become readily apparentfrom the following detailed description of the drawing in which:

Fig. l is a partial showing of a propeller blade illustrating the variedcontour of the trailing edge thereof;

Fig. 2 is an illustration in partial cross section of a propeller hubhaving a blade of variable contour;

Fig. 3 shows a typical cross section through the propeller blade of Fig.2; and

Figs. 4, 5 and 6 illustrate the various propeller contours for differentoperative conditions.

Referring to Fig. l, a typical propeller blade portion is generallyindicated at and includes upper and lower major surfaces 12 and 14. Atypical expanded boot 18 is illustrated so as to change the contour asseen by the line 20 adjacent the blade trailing edge to improve orincrease the lift of the propeller blade at low speeds. The boot 1Snormally lies ush with the lower major surface 14 of the propeller bladeas seen in Fig. 3, while another boot 22 normally lies llush with theupper major surface 12 of the blade. It is thus desired to have anon-off type of operation so as to improve the characteristics of thebasic blade configuration.

Thus, as seen in Fig. 2, a propeller hub is generally indicated at 30 ashaving a propeller blade 32 carried thereby. The blade is shown insubstantially feathered position for convenience of illustration of theinside thereof. The blade may be hollow or solid but includes a pair ofpipes 34 and 36 (see also Fig. 3), respectively, which lead to aplurality of linger-like feed lines 38 and 40. The lines 38 openupwardly to the underside of the boot 22, while the pipes 40 lead to theunderside of the boot 18. Fluid to the lines 34 and 36 is conducted fromsuitable sources of drain and pressure by means of valves 44 and 46,respectively, which are carried in from fixed part of the aircraft andmounted on nonrotatable structure. Fluid under pressure may betransferred from the valves 44 and 46 to the lines 34 and 36 in therotating propeller hub by any suitable means as, for example, shown inPatent No. 2,296,288 issued September 12,

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1942, to Martin et al. or in Patent No. 2,338,483 issued January 4,1944, to Beebe, Jr.

Thus, by contouring the valves 44 and 46, the boots 18 and 22 can beselectively inflated or deated to improve the lift characteristics andstall flutter boundary of the propeller for various operativeconditions.

The stall flutter boundary may be best described in connection with theproblem solved. The application of,

be used at the outerstations of the propeller blade.l

However, the use of these airfoil sections compromises the off-designoperating conditions because of the inherent lower stall angles of thesesections as compared to those of thick, high-camber propeller sections.Consequently, not only is the take-off thrust potential of the propellerreduced, but also the propeller becomes more susceptible to the singledegree-of-freedom instability known as stall flutter. That is to saywhen the blade operates stalled during all or a portion of its cycle ofoscillation, energy may be extracted from the airstream to maintainthese oscillations. Experience shows that these critical conditions arefunctions of the mean angle of attack of operation of the blade and theflow velocity. rhe particular critical points at specified angle ofattack and flow velocity combinations form the boundary between stableand unstable operating conditions-hence form the so-called Stall FlutterBoundary. Thus, as seen in Fig. 4, for normal high speed operation therelative air will be approaching the airfoil 48 in the direction of thearrow. In this condition both the boot 18 and the boot 22 are flush withthe outer airfoil surface to provide low drag at the high speedposition. On the other hand, as seen in Fig. 5, when the propellerblades are rotating at a relatively low speed and high positive thrustis desired, the boot 18 is expanded so as to vary the contour of onlyone of the major surfaces of the airfoil. It will be noted that althoughthe effect of a ap is obtained, a ap when moved varies the contour ofboth the upper and major surfaces of the airfoil.

Then, as seen in Fig. 6, where the relative air is as shown by thearrow, reverse thrust or lift is being provided by the airfoil and theboot 22 is expanded to provide good low speed air ow conditions.

The particular profile desired may be obtained by providing prestressedor variable stiffness boot material; or

the material may have a variable thickness to provide the l differencein stretch at different chordwise positions.

It should be noted herein that by applying the contour varying mechanismto the trailing edge, we obtain a higher lift at low angles of attack sothat the concept herein dilfers from devices which attempt to vary thecamber of the leading edge of airfoils. Leading edge devices areintended to obtain higher angles of attack for the basic airfoil beforea breakdown of liow occurs or stall ensues. Furthermore, higher anglesof deflection of the contour can be obtained from this type of device ascompared to leading edge mechanisms.

Furthermore, the reverse thrust stall flutter boundary of the devicedescribed herein will be much better than any leading edge cambermodification. When the blade operates at negative values of lift, we sayit operates in a reversed thrust condition. The flutter boundary curvesso defined at these negative values of lift are called the reversedthrust Stall Flutter Boundary.

As `a. result of this invention it is apparent that a very simple,easily operated-meanshas been provided for practically Varying thecontour of one of the major surfaces of a propeller blade adjacent thetrailing edge of the blade. With this device good low speed, high thruststall utter free characteristics-are*obtained at a minimum weightexpense.

Although only one embodiment of this invention lhas been illustrated anddescribed herein, it will become readily yapparent that various changesyand modifications may be made in the construction and arrangement ofthe various parts without departing from the scope of this novelconcept.

What is desired by Letters Patent is:

` In a propeller having a hub, a plurality of blades carried by said hubhaving upper and lower major aerody` namic surfaces, means for varyingthe camber of each of said blades including inllatable resilient bootsextending over a major part of the span of each of said blades and beinglocated adjacent the trailing edges thereof, said boots being located onsaid upper and lower major surfaces of said blades and extending overonly a minor portion of the chordwise dimension of said blades, saidtrailing edges normally being relatively sharp, said boots in thedeflated position lying substantially flush with the remainder of saidmajor surfaces, means for selectivelyy varying the contour of said bootsand thereby selectively usV altering'the contour of either the upper orlower surfaces respectively of all the blades simultaneously whereby thetrailing edge of each blade becomes relatively blunt and rounded foroperation in positive or negative pitch posi- -ton respectively, saidlasst-mentioned means including a source of fluid under pressure, alsource of relatively low pressure, nonrotatable means operativelyconnected to said sources, and means connecting said nonrotatable meanswith the interior of said hub including valving for simultaneouslyconducting fluid to or from said boots on the same side of all theblades.

References Cited in thel le of this patent UNITED STATES PATENTS2,011,902 Leigh Allg. 20, 1935 2,021,470 Upson Nov. 19, 1935 2,023,760Dornier Dec. l0, 1935 2,296,288 Martin et al. Sept.y 22, 1942 2,338,483Beebe Jan'. 4, v1944 2,400,388 Campbell May 14, 194.6 2,616,509 ThomasNov. 4, 1952 FQREIGN PATENTS. 617,058 Germany Aug. l0, 1935

